The present invention generally relates to a process for diffusing titanium and nitride into a base material. More specifically, a process is provided for diffusing titanium and nitride into a base material having a generally compact, granular microstructure (e.g., carbide).
The present invention relates to a low temperature process for diffusing titanium and nitride into a base material having a generally compact, granular microstructure in the presence of electrolyzed titanium. A low temperature process is preferred in that it prevents or lessens warping and twisting of the material, two disadvantages of conventional surface treatment processes. Titanium is considered a generally inert, light-weight material which has very high tensile strength (or toughness) and excellent corrosion resistance. Accordingly, because of their inert nature, increased hardness, increased tensile strength and increased resistance to wear, products containing titanium may be used in various applications including industrial, biomedical, aerospace, automotive, defense, jewelry, tools, tool-making, gun-making applications and other such applications.
Some materials having a generally compact, granular microstructure are known to be extremely hard and capable of withstanding high temperatures. Carbide is an example of one such material. Known carbides include, but are not limited to, boron carbide (B4C); chromium carbide (Cr3C2); iron carbide or cementite (Fe3C); niobium carbide (NbC or Nb2C); silicon carbide (SiC); tantalum carbide (TaC); titanium carbide (TiC); tungsten carbide (WC or W2C); vanadium carbide (VC); zirconium carbide (ZrC); ceramic carbide; any metal alloy containing carbide, and any other metal containing carbide. In one application of carbides, cutting tools containing such are generally used instead of high-speed steel or carbon steel tools to machine tough materials. In fact, cutting tools containing carbides may be used to machine carbon steel or other tough metals.
Nevertheless, carbides are generally more brittle than some metal materials or alloys, making them susceptible to chipping and/or breaking. For example, as illustrated in FIG. 1, carbides generally comprise a compact, granular microstructure. Although the granular microstructure contributes to the hardness of the carbide, among the grains 20 are small voids 22 which perpetuate the brittleness of the carbide structure. Accordingly, it is an object of the invention to provide a process for diffusing titanium and nitride into a material having a generally compact, granular microstructure to fill the voids inherent therein in order to further provide the enhanced properties of titanium therethrough (e.g., increased toughness or tensile strength).
U.S. Pat. No. 6,645,566, which is incorporated by reference herein and made a part hereof, describes a process for diffusing titanium and nitride into a variety of base materials including steel and steel alloys, aluminum and aluminum alloys, titanium and titanium alloys. Nevertheless, U.S. Pat. No. 6,645,566 does not describe a method for diffusing titanium and nitride into a material having a generally compact, granular microstructure or otherwise containing carbide. Carbides are generally known to be structurally different from other materials, metals or metal alloys. For example, as respectively illustrated in FIGS. 2, 3, and 4, steel, aluminum and titanium (the base materials described in U.S. Pat. No. 6,645,566) generally have an amorphous microstructure including an amorphous substructure 24 a, b and c having voids 26 therethrough.
The amorphous microstructure of steel, aluminum and titanium is markedly different from the generally compact, granular microstructure of carbide. The generally granular microstructure causes carbide to be generally harder than steel, titanium, and aluminum, which have generally amorphous microstructures. Moreover, the grains 20 of the carbide microstructure are generally more compact than the amorphous substructures 24 a, b and c of steel, aluminum and titanium. Accordingly, the voids 22 among the grains 20 of carbide are generally smaller than the voids 26 a, b and c among the amorphous substructure 24 a, b and c of steel, aluminum and titanium.
For materials such as steel, aluminum and titanium, the amorphous substructure 24 a, b and c and larger voids 26 a, b and c assist in the diffusion of titanium and nitride therethrough in the process as described in U.S. Pat. No. 6,645,566. In contrast, it is generally known that it is more difficult and nearly impossible to diffuse any substance into a material having a compact, granular microstructure such as carbide. Accordingly, it is an object of the invention to diffuse titanium and nitride into a material such as carbide to fill the voids inherent in its granular microstructure, despite its compact orientation, in order to provide the enhanced properties of titanium therethrough.
Other conventional surface treatment and coating processes for providing a protective layer on a base material or for strengthening materials have been applied to materials containing carbides. However, these processes are deficient in many respects. In one example, conventional surface treatments and coating processes have been typically applied to steel and steel alloys. Steel and steel alloys are generally known to contain a high content of iron. Some conventional nitriding surface treatment processes, such as in some Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD) and Ion Assisted Coating (IAC) processes, introduce nitrogen such that it reacts to iron in the steel or steel alloy to form a hardened ferrous nitride layer. This reaction causes the formation of a hardened ferrous nitride layer, which serves as a suitable protective layer on the base material.
These nitriding processes, however, are generally deficient when treating carbides. More specifically, carbides are generally known to contain a relatively low content of iron. As such, when applying these processes to carbides, there is generally not enough iron for nitrogen to react with. Accordingly, conventional nitriding surface treatments cannot generally form a hardened ferrous nitride layer on carbide due to its low iron content. Instead, a protective layer is formed which has a weak adhesion with the carbide surface, thereby causing it to be susceptible to chipping. It is therefore an object of the present invention to diffuse titanium and nitride into a material having a relatively low content of iron. It is further an object of the present invention to provide a process for strengthening the adhesion between a base material containing carbide and a protective layer formed by conventional surface treatments or coatings.